The present invention relates to an array type storage system made of WORM media such as WORM disks which inhibit once-recorded information from being updated.
A diskarray system is a storage system which is called a RAID (Redundant Arrays of Inexpensive Disks) system having a plurality of disk devices arranged in the form of an array, wherein a read request (data read request) and a write request (data write request) from a host machine are processed at high speed through the parallel operation of the disks, and redundant data is attached to data to improve the data reliability.
At present, such disk devices as hard disks whose data can be updated as necessary are generally employed as disk devices of a diskarray system. However, such a disk device as rewritable its data as necessary has a problem that the disk device cannot cope with unexpected user data destruction resulting, e.g., from a format command or the like entered by the operator or user of the host machine through his erroneous operation, or with intended user data destruction resulting, e.g., from a computer virus which is originally intended to destroy user data.
For the purpose of solving the above problem, there has been proposed a hard disk device which has a WORM (Write Once Read Many) function of enabling data writing operation only once, or in other words, disabling data updating (or overwriting). Such a WORM disk device is realized, for example, by providing a flag allowing writing operation to each sector in the disk device. A recording medium or media having such a WORM function, or a disk device or devices having the WORM function will be referred to merely as WORM drive or drives or WORM disk or disks, hereinafter.
Further, there has been developed a diskarray system wherein WORM media allowing writing operation only once such as CD-Rs are used.
With regard to the diskarray system, there is a technique for arranging data on a disk array as disclosed, e.g., in D. Patterson, et al: “A Case for Redundant Arrays of Inexpensive Disks (RAID)”, ACM SIGMOD conference proceeding, Chicago, Ill. Jun. 1–3, 1988, pp. 109–116. A technique for a diskarray system using a media such as CD-Rs allowing writing operation only once is disclosed in JP-A-7-13705. Also disclosed in JP-A-9-265714 is a technique of how to handle redundant data which becomes a problem in the diskarray system of a plurality of disk devices including at least one disk device having the redundant data stored therein.